Pin connections

[narges047]

I have a simple question, but I am not sure about the answer!

How I can define pin-pin connections for a nonlinear beam-column element (at both ends).

Your time and help is really appreciated

Please not that:

1) I have to use nonlinear beam-column element for my buckling model (so truss element is not working for me)

2) I can not use zero length element with low rotational values since I dont want messing up the stiffness matrix. (I want to analyze a big model with over 300 elements)

[hugo_esquivel]

You might want to use the equalDOF command. For examples of how to use it, look at the manual... the command has been very well documented and explained along the entire manual.

[narges047]

Hi hugo_esquivel,

I am afraid of using equalDOF. In all of pin connections moment is zero but rotations are the same? I think NO. So they could not be assumed as equalDOF. Thanks for your time and help

[hugo_esquivel]

Can you upload a figure describing how the pin connections will be modeled? I am quite sure that pin connections can be modeled --without losing any accuracy-- by just using equalDOFs... unless, of course, some rigidity is intended to be added on the pins. In such a case, they can be modeled by either using zero-length elements or mixing both implementations (zero-length elements plus equalDOFs).

[narges047]

Let me tell you something frankly. You are 100% wrong. What you tell me is that "in all of pin connections , for example a 1000 DOF structure, the rotation is same" and "if not, there will be a little accuracy problem".

I am simply not on your side.
thanks

[fmk]

you do use the equalDOF command, but you only constrain the translational dof to move together .. leave the rotational dof to move seperatly ..i.e. you leave the rotational dof alone .. here is an elastic example, elements 4 and 5 are braces:

[code]
model basic -ndm 2 -ndf 3


# Set parameters for overall model geometry
set width 360
set height 144

# nodes
node 1 0.0 0.0
node 2 $width 0.0
node 3 0.0 $height
node 4 $width $height

node 11 0.0 0.0
node 22 $width 0.0
node 33 0.0 $height
node 44 $width $height

# constraints
fix 1 1 1 1
fix 2 1 1 1
fix 11 1 1 0
fix 22 1 1 0

equalDOF 3 33 1 2
equalDOF 4 44 1 2

#geometric transformation
geomTransf Linear 2

# elements

###columns
element elasticBeamColumn 1 1 3 360 4030 8640 2
element elasticBeamColumn 2 2 4 360 4030 8640 2

### beam
element elasticBeamColumn 3 3 4 360 4030 8640 2

### braces
element elasticBeamColumn 4 11 44 360 4030 8640 2
element elasticBeamColumn 5 22 33 360 4030 8640 2

# loads
pattern Plain 1 "Linear" {
load 3 100.0 0.0 0.0
load 4 100.0 0.0 0.0
}

#analysis
system BandGeneral
constraints Transformation
numberer RCM
test NormDispIncr 1.0e-12 10 3
algorithm Newton
integrator LoadControl 0.1
analysis Static

#analyze
analyze 10

#output
print node 3 33
print ele 1 2 3 4 5
[/code]